Method of designing a soluble oil slug for an oil recovery process



O l'a ilioslic United States Patent US. Cl. 166-273 17 Claims ABSTRACT OF THE DISCLOSURE Micellar solutions having a relatively small hydrophilicy in the front portion thereof and a relatively large hydrophilicy at the back portion thereof are injected into and displaced through a subterranean formation to a production means in a secondary-type recovery process to displace crude petroleum therefrom.

CROSS-REFERENCE TO RELATED APPDICATION This application is a continuation-in-part of my copending US. patent application Ser. No. 671,978, filed Oct. 2, 1967 BACKGROUND OF THE INVENTION Micellar solutions are useful as flooding mediums, to displace crude petroleum in subterranean formations. Examples of such systems are taught in US. Patents Nos. 3,275,075, 3,254,714, and 3,261,399. Micellar systems of the past are generally designed to be either hydrophilic or oleophilic. The characteristics of the recovery processes within the formation are directly dependent upon the micellar solution characteristic, i.e. an oleophilic system tends to act more miscible with the crude oil in place whereas a hydrophilic system tends to act more miscible with the interstitial water in place.

If the sands within the formation, especially waterwet sands are contrasted to oil-wet sands, could be preferentially Wetted with an oleophilic fluid, more efficient sweeping of the formation fluids could be realized. Also, such a system would result in higher recovery yields of residual oil in place.

DESCRIPTION OF THE INVENTION Applicants have discovered that the percent recovery of crude oil in secondary-type recovery processes (includes any process wherein artificial means are used to displace the oil, e.g. tertialy recovery) can be improved by injecting as the primary oil displacing medium a micellar solution slug having a relatively small hydrophilicy in the front portion of the slug and a relatively large hydrophilicy in the back portion of the slug. The terms relatively small hydrophilicy and relatively large hydrophilicy define the degree of water capable of being incorporated by the primary oil displacing medium, e.g., the character of the micellar solution to take up water.

The micellar solution can be displaced through the formation by any compatible displacement fluid; for

il-n IHVUE ll 3,476,184 Patented Nov. 4, 1969 example, by a thickened water drive or by a combination of a thickened Water drive and a water drive. The thickened water drive can have graded mobilities from a low at the micellar solution juncture to a high at the water drive. However, the mobility of the front portion of the displacement fluid can be less than the mobility of the micellar solution and the average mobility of the displacement fluid between that of the micellar solution and that of the water drive. Examples of water drives are disclosed in U.S. Patent No. 3,261,399.

The primary oil displacing mediums useful with this invention are preferably oil external micellar solutions. The term micellar solution as used herein is meant to include microemulsions [Schulman and Montague, Annals of the New York Academy of Sciences, 92, pages 366-371 (1961)], oleotopathic hydro-micelles [Hear and Schulman, Nature, 152, page 102 (1943)], transparent emulsions (Blair, Jr. et al., US. Patent No. 2,356,205), micellar dispersions, and micellar solutions defined in US. Patents Nos. 3,254,714; 3,275,075; 3,301,325; and 3,307,628. Micellar solutions differ from emulsions in many ways, one of the strongest differentiations being that the former tend toward further dispersion of the internal phase rather than toward coalescence of this phase.

The micellar solution is composed essentially of hydrocarbon, aqueous medium, and surfactant suflicient to impart micellar solution characteristics to the mixture. Examples of hydrocarbon include crude oil, straight-run gasoline such as lower hydrocarbon fractions, crude column overheads, and liquefied petroleum gases. The aqueous medium is preferably water but can be brine or salty water and can contain corrosion inhibitors, bactericides, etc. Useful sufactants are listed in US. Patent No. 3,254,- 714 and preferably are alkyl aryl sulfonates, more commonly known as petroleum sulfonates or as alkyl aryl naphthenic sulfonates. Examples of useful petroleum sulfonates can be identified by the empirical formula C H SO M wherein n is an integer from about 20 to about 30 and M is a monovalent cation such as sodium, potassium, ammonium, etc.

Examples of useful surfactants which are more hydrophilic include dodecylbenzene sodium sulfonate, sodium laurylsulfate, fatty alcohol amine sulfonates, sorbitan tristearate, water soluble sodium sulfonates, partial sodium salt of n-lauryl beta iminodipropionate, condensate of ethylene oxide with hydrophobic base of propylene oxide and glycol, ethylene diamine tetracetic acid, and alkyl aryl polyethyleneoxy esters. The more hydrophilic sulfonates can be incorporated into the back portion of the micellar solution to increase the hydrophilicy.

Examples of surfactants which are more oleophilic include alkylphenol ethoxylate, bis (tridecyl) ester of sodium sulfonsuccinic acid, substituted oxazoline, sorbitan partial'fatty acids, natural lecithin, nonylphenol polyglycol ether alcohol, long'bliaifi'fatty acid esters of glycols, polyoxyethylated vegetable oils, polyethylene glycol oleic acid ester, nonylphenyl polyethylene glycol ester, etc. These surfactants are useful in the front portion of the micellar solution to impart a less hydrophilic character.

In addition, the micellar solution can contain a semipolar compound (co-surfactant or co-solubilizer) such as ketones, esters, amides, and alcohols containing from 1 up to 20 or more carbon atoms. The semi-polar compounds can be divided into two classes, i.e. hydrophilic HUM/M13 and oleophilic. Preferably, the semi-polar compounds are alcohols. Examples of hydrophilic alcohols include methanol, ethanol, isopropanol, nand isobutanol, and tertiary butanol. Examples of oleophilic alcohols include the amyl alcohols, hexyl alcohols (e.g. 1- and 2-hexanol, 1- and 2- octanol), decyl alcohols, cresols, and p-nonyl phenol.

Electrolytes are also useful within the micellar solutions. Such are defined as inorganic bases, inorganic acids, inorganic salts, organic bases, organic acids, and organic salts. Examples of useful electrolytes can be found in US Patents Nos. 3,297,084 and 3,330,343. Preferably, the electrolytes are inorganic acids, inorganic bases, and inorganic salts and are substantially water soluble. Preferred examples of electrolytes include sodium chloride, sodium sulfate, sulfuric acid, sodium hydroxide, hydrochloric acid, sodium nitrate, and similar potassium and ammonium salts.

Preferably, the micellar solutions consist of five components, i.e. hydrocarbon, aqueous medium, surfactant, electrolyte, and semi-polar organic compound. As mentioned earlier, the micellar solution is characterized as having a relatively small hydrophilicy in the front portion thereof and a relatively large hydrophilicy in the back portion thereof. Also, it is contemplated that the micellar solution can have a graded sorption zone from a minimum water uptake (i.e. relatively small hydrophilicy) in the front portion thereof to a maximum water uptake (i.e. relatively large hydrophilicy) in the back portion thereof. This can be accomplished by continuously grading the micellar solution as it is injected into the subterranean formation or can be eifected by injecting a series of micellar slugs wherein each slug is graded accordingly.

Characterizing the micellar solution from a relatively small hydrophilicy to a relatively large hydrophilicy throughout the solution can be effected by incorporating into the front portion an alkyl aryl naphthenic sulfonate having a molecular weight within the range of from about 440 up to about 520 (these molecular weights are less hydrophilic) and decreasing the molecular weight to the back portion of the micellar solution to a sulfonate having a molecular weight range of from about 360 up to about 460 (these molecular Weights are more hydrophilic). Molecular weights below about 360 are also useful within the back portion of the micellar solution. The molecular weights within the mid-portion of the micellar solution can be within the range of from about 400 up to about 500 and preferably within a proportionate range of the high and the low molecular weight ranges of the micellar solution.

The micellar solution slug can also be graded from a relatively small hydrophilicy in the front portion thereof to a relatively large hydrophilicy in the back portion thereof by incorporating a more oleophilic semi-polar organic compound in the front portion and a more hydrophilic or oleophobic semi-polar compound in the back portion of the slug. An example of such a system would be p-nonyl phenol incorporated in the front portion and isopropanol incorporated in the back portion of the micellar solution. Also, such a solution can have a semi-polar organic compound which is somewhat oleophilic and somewhat hydrophilic in the mid-portion of the micellar solution, e.g. tertiary butanol, amyl alcohols and 1- and 2- hexanol. Examples of semi-polar compounds which can form a graded slug, from front to rear are, in sequence, p-nonyl phenol, l-hexanol, and isopropanol.

The mobility of the front portion of the micellar solution can be about equal to or less than that of the crude petroleum or preferably about that of the combination of crude petroleum and interstitial water in the formation. Also, the mobilities at the interfaces of the crude petroleum and the micellar solution, the micellar solution and a subsequent thickened water drive, and the juncture of the thickened water drive and any subsequent Water drive can be about equal to protect against fingering.

Also, the micellar solution can be incrementally increased in mobility from a low at the formation fluids, i.e. crude petroleum and interstitial water, to a high at the subsequent drive material, e.g. thickened water drive.

The thickened water drive can have an average mobility between that of the micellar solution and that of the water drive. Also, the thickened water drive can have graded mobilities from a low at the micellar solution and thickened water drive juncture to a high at the thickened water drive and water drive juncture. Preferably, the front portion of the thickened water drive has a mobility about equal to or less than that of the micellar solution.

Normally, from about 1 up to about 20% of the formation pore volume of micellar solution is desirable to effect good oil recoveries and more preferably from about 3% up to about 10%. The amount of thickened water drive can vary from about 5% up to about 75% and preferably should be Within the range of from about 10% to about 50%, the percents based on pore volume of the formation. As mentioned earlier, the micellar solution can be divided into two or more parts to effect the graded characteristic, however, the combined total of parts should be within the above-identified percents of pore volume.

The following example is presented to illustrate a specific working embodiment of the invention. It is to be understood that the invention is not to be limited by the micellar solution compositions, the thickened Water composition, the percentages of the compositions, the operating conditions, etc. Rather, it is intended that all equivalents obvious to those skilled in the art be included within the scope of the invention as defined in the specification and appended claims. Percents, unless otherwise specified, are based on volume.

Example 1 Berea cores 47.5 inches long by 2 inches in diameter are cleaned to remove hydrocarbon and water, subjected to a vacuum to remove gas, flooded with water treated from the Henry lease in Illinois, (hereinafter identified as Henry plant Water, and contains about 9,700 p.p.m. chloride and 17,000 p.p.m. of total dissolved solids), flooded with Henry crude (an Illinois basin crude having an API gravity of about 36.4 and a viscosity of about 7 cps.) and are then flooded with Henry plant water to irreducible Water. Thereafter, micellar solutions defined in Table I are injected into the core samples.

TABLE I.MICELLAR SOLUTION COMPOSITIONS slug Slug slug on (0190- (hydro- (hydrophilic) philic) philic) Component percent percent percent Hydrocarbon:

Crude Column Overhead. 68. 06 56. 11

Henry Crude 27. 4

Aqueous Diluent:

Henry Plant Water Palestine Water Distilled Water. Surfactant:

Ammonium Alkyl aryl Naphthenic Sulfonate l 12. 72 1 10. 45 1 6. 7 Alconox 2 Semi-polar Compound:

Isopropyl Alcohol 1. 41 1. 43 0. 74 Nonyl Phenol 0 27 0. 56

Electrolyte: Sodium Hydroxide.

The slugs of micellar solution are followed by a thickened water drive composed of Water treated from the Palestine water reservoir in Palestine, Illinois (containing 500 p.p.m. of dissolved solids), 800 p.p.m. of 530 Pusher (sold by and a trademark of Dow Chemical Com- TABLE II 6 about 440 to about 520 and the back portion of the micellar solution contains alkyl aryl naphthenic sulfonate having a molecular weight within the range of from about 360 to about 460.

Core Characteristics Micellar Solution Crude Oil Recovery Perme- Oil Satu- Percent ability Porosity ration after Composi- Slug Size, Oil in (md.) (percent) Waterflood tion Type percent PV Place Percent Improvement 158 18. 2 1.371 A 60.4 87 17. 9 0. 364 B 63. O 78 16. 4 0.362 A/B 2 5 of A, then 83.1 Over Sample l=37.5.

2.6 of B. Over Sample 1=32.0. 82 17.3 0.368 A/B 2.5 of A, then 78.2 Over Sample 1=29.5.

3.75 of B. Over Sample 2=24.1. 98 18.2 0. 378 O 5.37 48. 8 164 19.3 0. 352 A/C 2.5 of A, then 66. 1 Over Sample 1=9.4.

2 5 of C. Over Sample 5=35.5.

Samples 3 and 4 (combination of oleophilic and hydrophilic slugs) compared to Sample 1 (oleophilic slug) and Sample 2 (hydrophilic slug) indicate the advantages of this invention. Sample 6 compared to Samples 1 and 5 also supports the novelty of the invention.

What is claimed is:

1. A process for the recovery of crude petroleum from subterranean formations wherein a micellar solution is injected into and driven through the formation to displace crude petroleum, the process comprising injecting into the formation a micellar solution having a relatively small hydrophilicy in the front portion of the micellar solution and a relatively large hydrophilicy in the back portion of the micellar solution.

2. The process of claim 1 wherein the front portion of the micellar solution contains relatively oleophilic surfactant and the back portion of the micellar solution contains relatively hydrophilic surfactant.

3. The process of claim 1 wherein the front portion of the micellar solution contains alkyl aryl naphthenic sulfonate having a molecular weight within the range of from about 440 to about 520 and the back portion of the micellar solution contains alkyl aryl naphthenic sulfonate having a molecular weight within the range of from about 360 to about 460.

4. The process of claim 1 wherein the front portion of the micellar solution contains oleophilic semi-polar compound and the back portion of the micellar solution contains hydrophilic semi-polar compound.

5. The process of claim 1 wherein the micellar solution is graded from front to rear with surfactant decreasing in oleophilicy from front to rear.

6. The process of claim 1 wherein the micellar solution is graded from front to rear with semi-polar compound decreasing in oleophilicy from front to rear.

7. A process for the recovery of crude petroleum from subterranean formations wherein fluids are injected into the formation through at least one injection means to displace the crude petroleum toward at least one production means, the successive injection steps comprising:

(1) a micellar solution characterized as having a relatively small hydrophilicy in the front portion of the micellar solution and a relatively large hydrophilicy in the back portion of the micellar solution,

(2) a thickened water drive, and

(3) a water drive in an amount sufficient to displace a micellar solution and a thickened water drive toward at least one production means and recovering crude petroleum therefrom.

8. The process of claim 7 wherein the front portion of the micellar solution contains oleophilic surfactant and the back portion of the micellar solution contains hydrophilic surfactant.

9. The process of claim 7 wherein the front portion of the micellar solution contains alkyl aryl naphthenic sulfonate having a molecular weight within the range of from 10. The process of claim 7 wherein the micellar solution is characterized as being graded from front to rear with surfactant decreasing in oleophilicy from front to rear.

11. The process of claim 7 wherein the front portion of the micellar solution contains oleophilic semi-polar compound and the back portion of the micellar solution contains hydrophilic semi-polar compound.

12. The process of claim 7 wherein the micellar solution is graded from front to rear by semi-polar compound decreasing in oleophilicy from front to rear.

13. The process of claim 7 wherein the front portion of the micellar solution contains oleophilic alcohol and the back portion of the micellar solution contains hydrophilic alcohol.

14. The process of claim 7 wherein the thickened water drive is characterized as having an average mobility between that of the micellar solution and that of the water drive.

15. The process of claim 7 wherein the thickened water drive is characterized as having graded mobilities from a low at the micellar solution and thickened water drive juncture to a high at the thickened water drive and water drive juncture.

16. The process of claim 7 wherein the micellar solution has a mobility about equal to or less than that of the combination of crude petroleum and interstitial water in the formation.

17. The process of claim 7 wherein the front portion of the thickened water drive has a mobility about equal to or less than that of the micellar solution.

References Cited UNITED STATES PATENTS 3,254,714 6/1966 Gogarty et al. 166-9 3,261,399 7/ 1966 Coppel 166-9 3,275,075 9/1966 Gogarty et al. 166-9 3,297,084- 1/1967 Gogarty et al. 166-9 3,301,325 1/ 1967 Gogarty et al. 166-9 3,307,628 3/1967 Sena 166-9 3,330,343 7/ 1967 Tosch et al. 166-9 3,348,611 10/ 1967 Reisberg 166-9 3,373,809 3/ 1968 Cooke 166-9 3,376,925 4/ 1968 Coppel 166-9 3,406,754 10/ 1968 Gogarty 166-9 STEPHEN J. NOVOSAD, Primary Examiner US. Cl. X.R. 166-275 

